Separation of para cresol from a liquid phenolic mixture



UNITED STATES PATENT OFFICE SEPARATION OF PARA CRESOL FROM A LIQUID PHENOLIC MIXTURE Frederick Comte, Webster Groves, Mo., assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. Application November 25, 1933, Serial No. 699,712

6 Claims. (Cl. 260-154) This invention relates to the separation of respective constituents is for practical purposes para cresol from a mixture of liquid phenolic almost impossible of attainment and renders the substances with which it is commonly associated process, as a whole, costly and of very little and which are not readily separable by ordinary commercial importance.

physical means. It represents an improvement The present invention has as its object the 60 on the well-known process for isolating para obviation and minimization of the foregoing discresol by means of oxalic acid described in Geradvantages and difiiculties. man Patent 137,584 of 1903 to Rutgers. I have found that of the several addition prod- The cresols which are obtained in commerce nets of oxalic acid formed in this process, the

10 are by-products of the destructive distillation of para cresol addition product is substantially 65.

coal and are recovered in their crude form physimore stable at moderately elevated temperatures cally admixed with phenol as well as several than other phenolic addition products of oxalic xylenols. Due to the differences in boiling points acid and that it is feasible to selectively remove it is possible to separate phenol, ortho-cresol and the contaminating addition products whereby a most of the xylenols, from the crude mixture. para cresol having a purity of 97% and better is 70 However, para cresol cannot be separated from directly obtainable. meta cresol and certain of the xylenols due to I have further found that the resolution of the fact that the boiling. points of these subthe addition product can be effected in the abstances are practically identical. For this reason sence of water and preferably in the presence other methods of separation have in the past of a non-aqueous, inert liquid solvent for para 75 been employed. Among these methods are those cresol. As a result of the resolution under these which depend upon the formation of a solid addiconditions one obtains a solution of para cresol tion compound with one of the constituents from in the solvent and solid anhydrous oxalic acid which the other constituent may be separated by which is in excellent condition for immediate physical means, after which the separated addireuse without further operations. 80

ticn compound is resolved into its components. The various non-aqueous solvents for para ore- One such method takes advantage of the fact sol may be employed such as benzol, toluol, carthat anhydrous oxalic acid combines with para bon tetra chloride, etc. However, I have obcresol to form a solid addition product which tained the best results both from the standpoint y be separat d om the liquid residue. Acof the purity of the product and economy of oper- 85 cording to this method the solid is resolved into ation with petroleum naphtha. For this purpose its constituents by the addition of a small quanetroleum naphtha which has a boiling range tity of water. The phenolic fraction may be that is sufliciently removed from that of para isolated from the oxalic acid solution by solvent sol to enable one to separate the same easily extraction or distillation. While this method by fractional distillation is to be preferred. A 90 enables one to Obtain a product W c i of naphtha having a substantially higher boiling distinctly higher para cresol content it does not range than para cresol may be emplo ed ive a p cresol i e tly but, on the contrary, cessfully and has the advantage of lowering the ives a product having not substantially o solvent losses. The preferred naphtha is one than para 1 This 15 Probably dueffio which boils substantially below the boiling point of A para Cr S 90-100 C. has been oun o e par icu ary combme also otherfihenoilc fi 9 efiective, although cuts which are substantially tabtly t? f%: gfg g gg f fi ggg ggi higher in boiling range but which nevertheless 45 t i tiai ed with certain disadvantages and are Sufficiently below the boiling point para gg i one of the principal disadvantages cresol to enable one to effect the separation of a by fractional nses from the f t that when the mixture thereof with para cresol and obstacles a distillation may be employed.

solid addition compound is treated with water I 50 two layers are formed 0115 an aqueous layer of The following example will serve to illustrate oxalic acid, the other an oily layer of para cresol. the application of the p m pl f y ntl nz The oily layer contains a substantial amount of kilos of finely ground y us a c cid water and oxalic acid dissolved therein. Furtherare mixed with 280 litres of petroleum solvent more, the aqueous layer contains some para naphtha having a boiling range of 90-100 C.

55 cresol. The separation of the layers into their The resultant mixture is heated to the boiling temperature. 216.6 kilos of cresol having the following weight ratio of ingredients:

Per cent Para. cresol 64.8 Meta cresol 32.9 Ortho cresol and xylenols 2.3

the liquid fraction and the crystalline product is I washed with fresh solvent in successive portions of approximately '75 litres each. One thus obtains 233 kilos of crystalline product. Assuming theaddition compound to consist of one mol of oxalic acid and two mols of para cresol, I employ 32%- excess of oxalic acid based on the amount of para cresol present in the mixture.

Onemethod of effecting resolution of the crystalline product into its constituents, according to the present invention, consists in boiling the crystals in 1500 litres of fresh solvent, filtering the, hot suspension, again treating the residue with 1500 litres of fresh boiling solvent, recovering the residue, and finally similarly treating the residue with 1220 litres of boiling solvent, and again filtering the suspension. The residue consists essentially of anhydrous oxalic acid which is in excellent condition to be used again in the first step of the process. The. combined filtrates yield 127 .5 kilos of cresol having a purity of approximately 92% para cresol.

If instead of boiling the original crystalline product with 1500 litres of solvent, as described hereinabove, one employs a lower temperature, for example Z0--80 C., or preferably a lesser quantity,.say 750 litres, of boiling solvent and keeps the filtrate thus obtained separate from the filtrate obtained in the two or three subsequent resolving operations, one resolves a preponderance of the impurities which are present in the form of oxalic acid addition products and thereby obtains a para cresol in the subsequent steps of the resolution which is of higher purity. In this way I have been able to obtain in good yields a para cresol of 96%98.5% purity. The precise temperature for the selective dissolution step will vary somewhat with the nature of the raw material and particularly the kind and amounts of phenolic substances which are present in the liquid phenolic mixture.

If desired, one may eifect the resolution of the addition compound by simply distilling off the cresol preferably at reduced pressure or with the aid of vapors of an inert, non-aqueous solvent such as benzol, petroleum naphtha, etc. which The constituents be employed decomposition will be more complete in fewer steps. If desired, one may effect the decomposition under pressure whereby higher temperatures are possible and pressure filtration may be employed advantageously to separate the residue from the solvent medium.

It is to be understood that the invention is not restricted to the particular phenolic composition described in the foregoing example but on the contrary it is applicable to compositions of widely varied nature. It is also to be understood that the conditions of the temperature, the boiling "range of the naphtha solvent, the amount of excess oxalic acid employed and other conditions of operation may be changed within the spirit of the present invention.

What I claim is:

ljIn the separation of para cresol from a liquid phenolic mixture containing the same by means of oxalic acid whereby a solid addition compound of para cresol and oxalicacid is formed which is separable from the liquid phenolic residue, the step of'resolving the separated addition compound into its constituents which comprises heating the same to its'decomposing temperature in the absence of water and below the decomposing temperature of the oxalic acid.

2. The method as defined in claim 1 and further characterized in that the resolution is effected with the aid of vapors of a non-aqueous substance which'in liquid form is. a solvent for meta cresol.

3. In the separation of para cresol from a liquidphenolic mixture containing the same by means of oxalic acid whereby a'solid addition compound of para cresol and oxalic acid is formed which is separable from the liquid phenolic residue, the step of resolving the addition compound into its constituents which comprises heating the same to its decomposing temperature in an inert, non-aqueous solvent for para cresol and inthe absence of water.

4 The method as defined in claim 3 and further characterized in that the solvent is a petroleum naphtha whose boilingrange is sufiiciently removed from the boiling point of para cresol to enable one to' effect separation thereof by fractional distillation.

5. The method as defined in claim 3 and further characterized in that the addition compound ucts of oxalic acid and phenols other than para cresol are formed as impurities, the step of separating the solid impurities before resolving the para cresol-oxalic acid addition product into its which comprises subjecting the crude mixture to selective resolution and dissolution of the foreign phenolic addition products, and subsequently decomposing the purified solid into para'cresol and oxalic acid.

FREDERICK COMTE.

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